As one of methods of forming a thin film such as a silicon nitride film on a semiconductor wafer (hereinafter referred to as “wafer”), a so-called ALD (Atomic Layer Deposition) method of sequentially supplying a thin film precursor gas and a reaction gas reacting with the precursor gas onto the surface of the wafer to laminate reaction products is known. As one example of a film forming apparatus for performing a film forming process using this ALD method, an apparatus is known in which a rotary table for revolving a plurality of wafers arranged in the circumferential direction is installed inside a vacuum container and a plurality of gas supply nozzles are installed so as to face the rotary table. In this apparatus, an isolation region to which an isolation gas is supplied to prevent the process gases from being mixed with each other is formed between the process regions to which the process gases are respectively supplied. Further, a region for activating a reaction gas by using plasma and a region for modifying a thin film by using plasma are formed apart from each other in the circumferential direction.
The above-described film forming apparatus is of a so-called semi-batch type in which a plurality of substrates is mounted on the rotary table to perform a film forming process, and has advantages of providing substrates with good in-plane uniformity and an increased throughput. In the industry, however, it is desired to further improve the productivity in the apparatus of such type.
There has been also conventionally proposed an apparatus in which four semiconductor target substrates are mounted and an upper region of a rotatable table is divided into four regions by partitions. This proposed apparatus may be effective in terms of a self-saturation reaction such as the ALD, but it does not manifest its operation method and does not suggest the present disclosure.